Replay-aware token measurement through the singleton ctx.tokenMeter service. It advances one isolated fold per session from the durable log, so compaction and other pressure-sensitive plugins can share accounting without depending on CompactService.

Configuration

Key	Default	Contract
`contextWindow`	`128000`	Positive integer service-wide context capacity.

The estimator intentionally uses one fixed heuristic: four characters per token plus structural overhead for roles, blocks, and request-envelope fields. contextWindow is the only deployment setting. Direct construction validates it; Loader mounts first apply the package's Schemastery shape validation.

Measurement contract

ctx.tokenMeter directly exposes three operations:

measure(session, requestHeader?) returns scalar request pressure at one consumed-log revision.
measureSurface(session) returns current surface nodes and their per-node prices at the same kind of revision.
estimateMessage(message) prices one message with the fixed heuristic.

Measurements are detached and deeply immutable. A caller that needs a consistent scalar/surface decision compares their logRevision values instead of copying the full history on every read.

The fold tracks request headers and deltas, step boundaries, surface appends and replacements, successful assistant messages, provider usage, and assistant-chunk provenance. Provider usage is reused only when the latest successful call's canonical request envelope matches the measured envelope; a later success replaces the earlier anchor. Otherwise the complete current envelope and surface are estimated. Surface changes remain signed relative to a matching anchor, including negative deltas after shrinking replacements.

Usage accounting sums disjoint input, cache-read, cache-write, and output buckets; reasoning is not added again. Every successful call records an assistant anchor, including content-less calls. An explicit empty provenance list means a known empty provider stream, while absent legacy provenance conservatively treats the durable assistant output as provider output.

Composition

- name: '@deepseek-ai/dsh-token-meter'
- name: '@deepseek-ai/dsh-compact-basic'

Both plugins have usable defaults. A deployment with a different capacity configures the meter once:

- name: '@deepseek-ai/dsh-token-meter'
  config:
    contextWindow: 32768

Model Experience

Indirectly, through consumers such as dsh-compact-basic; the service itself adds no prompt, message, schema, tool, or model call.

Known Limitations and Deferred Work

The fixed heuristic is approximate — content without reusable provider usage is priced by character count plus structural overhead, not an exact provider tokenizer or request serializer.
Provider usage is only reusable for an identical canonical envelope — prompt, prefix, tools, model, or call-config changes deliberately fall back to full heuristic estimation.
Legacy provenance is conservative — assistant messages without sourceEventSeqs cannot distinguish provider output from listener rewrites, so the fold avoids claiming a known empty or exact chunk stream.